Lightning Diverter for Conducting a Lightning-Induced Electrical Current and a Method of Producing the Same

ABSTRACT

The present invention concerns a method of producing a lightning diverter for conducting a lightning-induced electrical current, which is to be placed on structures such as wings on wind turbines, aircraft components, radomes and the like with the purpose of lightning protection. The method comprises the steps of making a plurality of holes in a plate of an electrically conductive material, filling said holes at least partly with one or more electrically non-conductive materials, and then finally dividing the plate—preferably into strips. The lightning diverter obtained hereby consists of a layer of electrically non-conductive material with a plurality of isolated segments of electrically conductive material. 
     The invention further relates to a diverter strip with isolated segments of concave shapes being advantageous because of the good connection between the segments and the non-conductive material.

The present invention relates to a method of producing a lightningdiverter for conducting a lightning-induced electrical current and to beplaced on structures such as wings on wind turbines, aircraftcomponents, radomes and the like with the purpose of lightningprotection. The present invention further relates to the design of alightning diverter strip.

BACKGROUND OF THE INVENTION

The increasing development in the field of wind energy plants isreflected in large units with still higher towers and longer bladesresulting in the increased risk of being struck by a lightning. Theplants are typically secured from lightning strokes, so that a possiblelightning current is attracted and led to the ground in a controlledmariner in order not to damage the sensitive elements in the wind energyplant. One of the most popular methods for securing lightning is byinstalling one or more so-called lightning receptors, which areconductive elements, and which are placed e.g. on the tip of the bladeand connected to internal conducting cables in the blades. This is e.g.known from EP 0783629.

A similar method has been described in U.S. Pat. No. 6,457,943 accordingto which a wind turbine blade is constructed with long parts of carbonfibre material in the total length of the blade. The carbon fibres,which are conductive, are thus acting as a lightning receptor, and thelightning current is led through the material and down into internallyplaced conducting cables. This method thus relates to the constructionof the entire blade, and it not only requires the use of carbon fibresin large parts of the blade, which is not always desirable, but also aspecific thickness of the carbon fibre parts so that the material canlead the lightning current without being damaged.

The blades are usually the longest part of the wind energy plant, andthey therefore have an increased risk of being struck by a lightning.Wind energy plants are placed in e.g. large numbers in the sea in theform of windmill farms, resulting in the fact that service andmaintenance becomes rather expensive and complex due to weatherconditions and difficult access conditions. Salt from the air depositson e.g. the blades, thus making these conductive, which again increasesthe risk of these being struck by a lightning.

In WO 01/77527 it is suggested to glue or tape strips of copper stringson to the blades and connect the strings to the receptors. The stringsare intended to conduct a lightning current to a receptor, from where itcan be led to the ground via a cable. This implies that the strings havesufficient conductivity in order to be able to hold a lightning currentwhich may exceed 50 kA. The strings must be exchangeable after strokesof lightning due to the damage caused by the strong heating resultingfrom the lightning current, which not only means monitoring of the windenergy plant and standstill during change, but also big expenses. Thereis furthermore the risk of the strings getting loose and consequentlyaffecting the aerodynamic properties of the blade negatively. Thestrings must otherwise be made of a heavy material, resulting inundesired extra weight on the blade. One of the problems when designinglong blades is to lower the weight, in that the weight in itself notonly makes the blades even heavier, but also the hub, the nacelle andthe tower.

Aircrafts are also exposed to lightning strokes and must therefore besecured from these. Aircrafts are equipped with radar installations,e.g. in connection with navigation, which are often placed in the noseof the aircraft in order to be able to look ahead. When radar equipmentis placed in the nose of the aircraft, the nose is not made fromaluminum like the remaining part of the aircraft. Rather, it is made ofa certain plastic material, as the radar otherwise would be unable tosee through the nose. The nose must also be secured from lightningstrokes, but it must be done in a specific way in order not to disturbthe radar. Since the 1960's, the idea of lightning protection by meansof so-called lightning diverter strips, which may be of differentshapes, has been known. One example is seen in U.S. Pat. No. 4,237,514,where a base, supplied with aluminum powder, is glued on to e.g. thenose of an aircraft in strips. The aluminum powder does not constitute acontinuous conductor, but rather disrupted or segmented, conductiveparticles. When these metallic and conductive particles are exposed to astrong electrical field as the result of a lightning stroke, shortcircuit among the particles takes place, and a conductive ionizedchannel is created in the air above the particles in which the currentlightning can be led to e.g. some metal part of the aircraft. Instead ofaluminum powder, U.S. Pat. No. 4,506,311 describes button- ordiamond-shaped metal pieces, which are separately incorporated into abase shaped as a ribbon. Both ribbons and strips are intended forinstallation outside of the nose of the aircraft, where they are placedsymmetrically radiating from the tip of the nose. Such a positionprovides a good protection, but at the same time it results inaerodynamic disturbance. Furthermore, these strips have thedisadvantages of not lasting very long, as the segments easily getripped off the base into which they are incorporated, either by thelightning or by simple wear. Therefore, these ribbons often need to berenewed when having been exposed to lightning. However, in manyapplications this is very costly and impractical. Diverter stripsaccording to U.S. Pat. No. 4,506,311 are furthermore seen to have theproblem that the lightning current can jump from underneath the segmentsto the next, which increases the risk of the current jumping into thestructure, which should be protected by the diverter. Anotherdisadvantage is that the strips are difficult to fasten onto thesurfaces without unwillingly stretching the strips or ribbons a little,thereby changing the distances between the segments accordingly. Thisagain changes the lift-off capacity of the strip as well as making smallopenings in the material where water can penetrate and startdeterioration of the material.

OBJECT AND SUMMARY OF THE INVENTION

It is therefore an object of the present invention to present asegmented diverter strip with a longer life-time than existing modelsand with as low as possible lift-off capacity to be an effectivelightning conductor, and yet on the same time being simple and easy toplace even on curved surfaces. It is a further objective to describe amethod of production of diverter strips, which is cost effective butalso provides high accuracy as to the spacing of the segments and theiradhesion to the layer underneath.

The invention describes a method of producing a lightning diverter forconducting a lightning-induced electrical current to be placed onstructures such as wings on wind turbines, aircraft components, radomesand the like with the purpose of lightning protection. The methodcomprises the steps of making of a plurality of holes in a plate ofelectrically conductive material, filling said holes at least partlywith one or more electrically non-conductive materials, and thendividing the plate, whereby a layer of electrically non-conductivematerial with a plurality of isolated segments of electricallyconductive material is obtained.

The invention described by the above is advantageous in that it ispossible to produce one or more diverter strips with high precision andvery low tolerances. It is possible to control all important parametersof the product such as the distances between the segments of theresulting diverter strip, the surface area and quality of the segments,the thickness of the layer of non-conductive material underneath thesegments, and the adhesion of the segments to the non-conductionmaterial—parameters that are all very important to the quality andeffectiveness of the final diverter strip. On the same time the methodof production according to the invention does not require any specialfacilities or machinery for the production and is a fairly simple andcost-effective process. Furthermore, it is simple to change theparameters in the process—for instance to produce diverter strips withdifferent shapes of the segments or of a different thickness.

The invention further relates to a method of producing a lightningdiverter according to the above description where the plate is dividedinto strips. By dividing the plate into strips as one of the last stepsin the method of production it is obtained that it is not a number ofisolated segments that have to be handled and arranged in the productionprocess, but instead a plate with holes. In this way the positioning ofthe segments in the adhesive becomes a fully controlled process, whichto a large extent ensures the quality of the final diverter strips.

Furthermore, the invention relates to a method of producing a lightningdiverter according to the above where the holes in the plate are made bycutting, preferably by laser cutting or by punching. These productionmethods are advantageous as they are fast, but still it is possible tocut the holes in the plate in the desired pattern with a high degree ofprecision and with the possibility to make as well sharp as roundcorners.

In one embodiment of the invention the electrically conductive materialis preferably a metal—such as stainless steel, brass, copper, brasscoated with nickel or varnished copper. Metals are in general materialswith good electrical conducting properties and are thus advantageous.Metals with a low tendency to oxidation by the surrounding air arepreferable. Further, metals have a high resistance to the wear that thediverter strip on an exposed surface is subjected to.

In another embodiment of the invention the electrically non-conductivematerial is preferably an adhesive—such as MS Polymer, or athermoplastic material or rubber. An adhesive is advantageous in that itis possible to obtain a good connectivity between the segments and thenon-conductive material. This partly ensures that the segments stay inplace and do not fall off or get ripped off by the lightning current,which would otherwise decrease or even destroy the functionality of thediverter strip. Furthermore, the mentioned materials are non-expensivematerials and with good production properties in relation to the methodof production described by the invention. The adhesives mentioned alsopose a high flexibility, which ensures that the resulting diverter stripcan be applied equally well to curved or uneven surfaces. Also thementioned materials all have good resistance to ultraviolet light andboth high and low temperatures, thereby ensuring a longer life-time. Yetanother advantage is the possibility to color the adhesive according tospecific wishes.

The invention further relates to a method of producing a lightningdiverter according to the earlier description, where the holes in theplate are at least partially filled by pressing the plate down into alayer of electrically non-conductive material. This describes a simpleway to both embed the segments into the adhesive and to ensure that theadhesive fully surrounds all the segments.

The invention also describes a method of producing a lightning diverteraccording to the above, and where the method further comprises applyinga layer of material increasing the stiffness of the lightning diverterin the direction along the strip and a further layer of electricallynon-conductive material to the first layer of electricallynon-conductive material. Hereby is by simple means obtained that theresulting diverter strip is not easily stretched along its longitudinaldirection for instance during the application of the strip to a surface.Such a stretching is to be avoided as this would change the distancesfrom one segment of conductive material to the next, thus changing thespark-over voltage and lift-off capacity of the strip. On the otherhand, the production method described above does not change the abilityof the lightning diverter strip to be applied onto uneven surfaces anddoes not increase the cost of the process significantly.

In an embodiment of the invention the method of producing a lightningdiverter as described above further comprises applying a double sidedadhesive tape to the outermost layer of electrically non-conductivematerial. This double sided adhesive tape eases the application of thelightning diverter strip to the surface it is to protect from lightning.Furthermore, the tape can be used during the manufacture to bettercontrol the process by guiding the tape on a solid support.

The present invention furthermore describes a lightning diverter forconducting a lightning-induced electrical current and to be placed onstructures such as blades on wind turbines, aircraft components, radomesand the like with the purpose of lightning protection, where thediverter comprises a layer of electrically non-conductive material witha plurality of isolated segments of electrically conductive material,and where the exposed parts of said segments are described by concaveshapes. Hereby is obtained a lightning diverter where the concave shapesby having larger circumferences increase the connectivity of thesegments to the non-conductive material significantly. This connectivityin turn prolongs the life-time of the diverter, as the segments do notget ripped off, neither by common wear nor by the lightning currents.The good connectivity further ensures that the lightning induced currentcan not run down into the structure onto which the diverter is fastened,and further prevents the penetration of water, which would otherwisereduce the life-time of the diverter.

In a further embodiment of the invention a lightning diverter accordingto the above is in the shape of a strip. Hereby the lightning inducedcurrent can be guided in the direction of the strip to for instance somekind of receptor connected to grounding means. A strip is furthermoreeasy to orientate on a surface according to specific needs.

In yet a further embodiment of the invention a lightning diverteraccording to all or some of the above is characterized by a number ofthe isolated segments being cross-shaped or star-shaped. These shapesare advantageous in that their connectivity to the surrounding materialcan be optimal. Furthermore it can be well controlled where the sparkswill jump from one segment to the next whereby the diverter can bedesigned to obtain a specific optimal spark-over voltage. Theses shapesmake it possible to obtain a diverter with a low spark-over voltage aswell as lift-off capacity, which is favorable in most applications. Alsothese shapes are advantageous in that the diverter strip then can bemanufactured using the method of production also described by thisinvention.

In one embodiment a lightning diverter according to the invention canalso comprise a layer of material increasing the stiffness of thelightning diverter in the direction along the strip. Hereby is by simplemeans obtained a diverter strip, which can not easily be stretched inits longitudinal direction, whereby it is assured that the distancesbetween the segments remain unchanged during application of the diverterto surfaces. This is important as these distances define the lift-offcapacity of the strip, and thus a change will change the qualities ofthe diverter accordingly.

A lightning diverter according to the invention can in anotherembodiment comprise an outermost layer of double sided adhesive tape.Hereby is obtained a diverter, which is ready and easy to be applied toa surface. This further increases the quality of the diverter as a goodfastening of the diverter to the exposed structure is essential for itsfunctioning and increases its lifetime.

The invention further relates to a lightning diverter according to someor all of the above, where the segments are preferably made of metalsuch as stainless steel, brass, copper, brass coated with nickel orvarnished copper, and/or the electrically non-conductive material ispreferably made of an adhesive such as MS Polymer, or a thermoplasticmaterial or rubber. The advantages hereof are as described above for themethod of production.

Finally, the invention describes a blade for a wind turbine, the bladecomprising a fibre-reinforced blade shell and means for grounding alightning-induced electrical current, where the blade is equipped withat least one diverter strip produced according to one or more of theembodiments mentioned above. Hereby is obtained a blade with the sameadvantages as described above for a diverter strip produced by a methodaccording to the invention, including that the blade is capable ofwithstanding a number of lightning strikes, as the lightning inducedelectrical current is conducted in a ionized channel in the air abovethe diverter strip, as well as the diverter strips being of low weight,that the diverter strips are not prone to crack etc.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following, preferred embodiments of the invention will bedescribed referring to the figures, where

FIG. 1 shows a plate of metal with a pattern cut into it for theproduction of a diverter strip,

FIG. 2 shows one embodiment of a diverter strip as described by theinvention,

FIG. 3 illustrates the steps in a method of producing a diverter strip,

FIG. 4 shows a diverter strip with a layer of double sided tape,

FIG. 5 shows the steps in a further method of producing a diverterstrip,

FIG. 6 shows another embodiment of a diverter strip according to theinvention,

FIG. 7 shows yet another embodiment of a diverter strip according to theinvention,

FIG. 8 shows different segment shapes for use in the diverter strip,

FIGS. 9 and 10 show two different plate designs with different patternsfor use in the manufacture of diverter strips,

FIGS. 11 and 12 show a part of a blade for a wind turbine with diverterstrips on the surface of blade.

DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 shows a plate 101 used in the production of a lightning diverteras described in the following. The plate 101 is made of a material withgood electrically conducting properties, preferably a metal such asstainless steel, copper, brass or the like. A number of holes 102 is cutinto the plate 101 e.g. by laser cutting or punching. The holes 102 areapplied in a pattern designed so that the plate can be divided into oneor more strips 103 as shown by the hatched lines 104 in the figureswhere the strip will then consist of a number of segments 105 all spacedapart and not connected. The strip 103 does not necessarily have to bestraight, but can be in any desired curved shape suitable for itspurpose. In the embodiment of the plate as shown in FIG. 1 the resultingdiverter will be a strip with a number of cross-shaped segments.Different patterns are shown in FIGS. 9 and 10.

Before the plate 101 is divided, the holes are filled with anelectrically non-conductive material preferably an adhesive such as MSPolymer. It could also be a thermoplastic material or a rubber. Thismaterial is then left to cure. The result after cutting the plate intostrips is one or more diverter strips as shown in FIG. 2 in perspectiveand as seen from the side consisting of a layer of electricallynon-conductive material 201 into which is placed a plurality of segmentsof electrically conductive material 105. In this embodiment of theinvention the segments 105 are shaped as crosses, which are advantageousas the attachment of the segments 105 to the non-conductive material 201thus is optimal. Other shapes are shown in figures in the following. Thesegments are exposed on the upper side and will act as attracters to alightning. As the segments are isolated, and do not touch each other,the air above the strip will be ionized, and the lightning current willrun in an ionized channel above the diverter strip. It is important forthe efficiency of the diverter strip that the segments are fully coveredby non-conductive material underneath, so that the current induced bythe lightning can not run down-wards into the structure. Also, thefairly sharp corners 202 at the end of the crosses facilitate the jumpof the lightning current from one segment to the next. Such corners willthus lower the spark-over voltage as well as the lift-off capacity ofthe strip. On the other hand, the inner corners in the crosses 203 arerounded in order to minimize the risk of crack formation from thesecorners.

The shape of the segments in one diverter strip can also vary along thelength of the strip. Another dimensioning parameter for a diverter stripis the distance or the gap 204 between the segments. The smaller thedistance the lower the spark-over voltage of the strip. Therefore, asmall distance is advantageous. On the other hand a too small a distancecan result in the lightning current running through the strip which isto be avoided. In one embodiment of the invention the distances betweenthe segments 204 are varied along the length of the strip which startsthe desired ionization of the air above the diverter strip sooner thanif the segments were all placed with the same distances. Such avariation is furthermore seen to result in a diverter strip with alonger lifetime. The sizes of the distances between the segments 204 liein the range of 0.1 to 5 mm, preferably 0.3 to 1.5 mm.

A method of producing the described diverter strip is illustrated inFIG. 3 as seen in a cross-sectional view. It consists of applying alayer 301 of electrically non-conductive or insulating material to aflat surface 302. If a MS polymer is used the production is performedwith heated tools in order to better control the processes. A plate 101with a number of holes 102 in a pattern such as the one shown in FIG. 1is then simply put on top of the layer of insulating material allowingthe adhesive to fill the holes at least partly for instance by applyinga slight pressure to the plate pressing it down into the adhesive asillustrated by the arrows 303. It is important for the efficiency of thediverter to ensure that the plate is fully covered by the insulatingmaterial 301 underneath. In one embodiment of the method the plate 101is grinded and pickled before use in order to further improve theconnection between the plate 101 and the adhesive 301. In a furtherembodiment of the production method yet a thin layer of the adhesive isapplied on top of metal plate in order to ensure that the segments areto be fully surrounded by/embedded in the adhesive. The material is thenleft to harden or cure. If a MS Polymer is used it will cure by means ofthe moisture from the air. The surface is then afterwards polished down,so the surface of the metal plate is exposed and open to the elementsand free to attract the lightning. In one embodiment of the method ofproduction the surface is further washed or rinsed, so that it istotally free of any dust from the polishing, and the center of eachstrip is then covered with a tape for protection of the clean surface(not shown in the figure). The product is then divided into oblongstrips, e.g. by cutting, and the strips are then ready to apply tostructures to be protected from lightning. The tape protecting the cleanand polished segments is to be removed when the diverter strip has beenfastened to the exposed structure. Because of the flexibility of theelectrically non-conductive material, the strip can easily be fastenedwith a good connectivity onto curved surfaces of structures.Furthermore, the flexibility of the strips ensures that the strip canfollow the deflections and the working of the structure, onto which itis fastened, whereby the efficiency and the lifetime of the diverterstrip are prolonged. The manufacture can also be turned upside down inthe sense that the resulting upper surface is pointing downwards duringthe production. The plate 101 is then first laid down next to the flatsurface 302, and then the layer of non-conductive material 301 isapplied both filling up the holes 102 in the plate 101 and forming thelayer insulating the segments from the structure in the resultingdiverter strip.

In order to ease the fastening of the diverter strip to structures, alayer of double sided adhesive tape 401 can be attached underneath thediverter. Such a diverter strip 103 is shown in FIG. 4. Duringmanufacture, the adhesive tape can then be laid down as a first stepthen applying the layer of non-conductive material on top etc. asexplained above.

In another embodiment of the method according to the inventionillustrated in FIG. 5, the diverter is further comprising a tissue 501underneath the metal plate 101. The method then consists of thefollowing steps: laying out the double sided tape 401 (optionally),applying a layer of adhesive 301, Then applying the tissue 501, and thena further layer of adhesive 502 followed by pressing the plate ofconductive material 101 gently down into the adhesive 502. Finally, afinal thin layer of adhesive (not shown) can be applied over the plateto ensure filling up the holes 102 in the plate completely. The productis then left to cure, and afterwards the upper surface is polished toexpose the segments and cleaned. As described before, a tape can thenalso be applied to protect the surfaces of the segments. The combinedplate is then finally divided or cut into strips. The tissue 501 couldfor instance be a thin glass fabric. The tissue 501 serves to make thestrip unstretchable in its longitudinal direction to ensure that thespacing of the segments and hence the lift-off capacity of the strip arekept unchanged during handling and fastening of the diverter strip. Onthe other hand, the tissue 501 does not alter the flexibility of thestrip and its ability to be optimally connected to curved and unevenstructural surfaces.

The FIGS. 6-8 illustrate different shapes of the segments 105 of theconductive material in the diverter strips 103 according to theinvention. In general the segments 105 can have any concave shape as forinstance cross-shaped as in FIG. 6, shaped as a star, as a ‘hen feet’(as sketched in FIG. 7), or potato-shaped. Different embodiments areillustrated in FIG. 8. The shape of the segments in one diverter stripcan also vary along the length of the strip. Their concave (ornon-convex) shape increases the attachment between the segment 105 andthe surrounding non-conductive material 201 partly because of the largercircumference of the segments. As described earlier, a corner(preferably sharp) is advantageous where one segment is the closest toits neighboring segment, as this is where the current will jump from theone segment to the next. Such a corner will thus lower the spark-overvoltage of the strip. Another dimensioning parameter for a diverterstrip is the distance or the gap between the segments. The smaller thedistance the lower the spark-over voltage of the strip. Therefore, asmall distance is advantageous. On the other hand, a too small distancecan result in the lightning current running through the strip, which isto be avoided. In one embodiment of the invention, the distances betweenthe segments are varied along the length of the strip, which starts thedesired ionization of the air above the diverter strip sooner than ifthe segments were all placed with the same distances. Such a variationis furthermore seen to result in a diverter strip with a longerlifetime. In a further embodiment of a diverter strip the segments reachout a little from the surrounding non-conductive material, therebyacting as more visible attracters to a lightning.

FIGS. 9 and 10 show two other design possibilities for the conductiveplate 101 to be used in the manufacture of the diverter strip asdescribed earlier. Only parts of the plates are shown. The plates arefilled at least partly with a non-conductive material in some way, andthen divided into strips as shown by the hatched lines 104. The patternof the holes 102 in both plates is so that the resulting diverter strips103 will contain segments 105 spaced apart in the shapes of crosses inboth figures but oriented differently.

FIG. 11 shows a blade for a wind turbine, which comprises a blade shell1001 with reinforcements 1002. The blade shell 1001 comprises an outersurface 1003, which is furnished with diverter strips 103. The diverterstrips 103 are placed in lengths and linked to grounded conductingcables. The diverter strips 103 are in FIG. 11 placed so that theyradiate from a receptor 1005, which is connected to conducting cables(not shown), which can be grounded to earth. The diverter strips 103 canrun primarily transversely to the blade 1001 in between the leading edgeand tailing edge of the blade, or they can be placed in the shape of astar as sketched in the figure. In the embodiment of FIG. 11, thediverter strips 103 have an antenna-like effect to any conductivefibres, which might be present in the blade shell 1001.

FIG. 12 shows a blade for a wind turbine, which comprises a blade shell1001 with reinforcements 1002. The blade shell 1001 comprises an outersurface 1003, which is furnished with diverter strips 103. The diverterstrips 103 are placed in lengths and radiate from a receptor 1005, whichis connected to conducting cables (not shown), which can be grounded toearth. In FIG. 12, the diverter strips 103 primarily run transversely tothe blade 1001 in between the leading edge and tailing edge of theblade. In an embodiment, the blade shell comprises two principallaminates 1101, which contain conductive fibres, such as carbon fibresor stell fibres. The upper principal laminate 1101 has a width asindicated by the hatched lines 1102. As illustrated, a diverter strip103 stretches from a receptor 1005 and across the principal laminate1101, so that it is shielded from a lightning stroke in that anantenna-like effect is acheieved by the diverter strip. In theillustrated embodiment the receptor 1005 is placed at a distance fromthe principal laminate 1101.

I should be noted that the above-mentioned embodiments illustrate ratherthan limit the invention, and that those skilled in the art will be ableto design many alternative embodiments without departing from scope ofthe appended claims. In the claims, any reference signs placed betweenparentheses shall not be construed as limiting the claim. The word‘comprising’ does not exclude the presence of other elements or stepsthan those listed in a claim. The invention can be implemented by meansof hardware comprising several distinct elements, and by means of asuitably programmed computer. In a device claim enumerating severalmeans, several of these means can be embodied by one and the same itemof hardware. The mere fact that certain measures are recited in mutuallydifferent dependent claims does not indicate that a combination of thesemeasures cannot be used to advantage.

1. A method of producing a lightning diverter for conducting alightning-induced electrical current and to be placed on structures suchas wings on wind turbines, aircraft components, radomes and the likewith the purpose of lightning protection where the method comprises thesteps of: making of a plurality of holes (102) in a plate (101) of anelectrically conductive material, filling said holes (102) at leastpartly with one or more electrically non-conductive materials, dividingthe plate (101), thereby obtaining a layer of electricallynon-conductive material (201) with a plurality of isolated segments ofelectrically conductive material (105).
 2. A method of producing alightning diverter according to claim 1 where the plate is divided intostrips (103).
 3. A method of producing a lightning diverter according toclaim 1 where the holes (102) in the plate (101) are made by cutting,preferably by laser cutting.
 4. A method of producing a lightningdiverter according to claim 1 where the holes (102) in the plate (101)are made by punching.
 5. A method of producing a lightning diverteraccording to claim 1 where the electrically conductive material ispreferably a metal.
 6. A method of producing a lightning diverteraccording to claim 1 where the electrically non-conductive material ispreferably an adhesive.
 7. A method of producing a lightning diverteraccording to claim 1 where the holes (102) in the plate (101) are atleast partially filled by pressing the plate (101) down into a layer ofelectrically non-conductive material (201).
 8. A method of producing alightning diverter according to claim 1 where the method furthercomprises applying a layer of material (501) increasing the stiffness ofthe lightning diverter in the direction along the strip (103) and afurther layer of electrically non-conductive material (502) to the firstlayer of electrically non-conductive material (301).
 9. A method ofproducing a lightning diverter according to claim 1 where the methodfurther comprises applying a double sided adhesive tape (401) to theoutermost layer of electrically non-conductive material.
 10. A lightningdiverter for conducting a lightning-induced electrical current and to beplaced on structures such as blades on wind turbines, aircraftcomponents, radomes and the like with the purpose of lightningprotection, where the diverter comprises a layer of electricallynon-conductive material (201) with a plurality of isolated segments ofelectrically conductive material, (105) and where the diverter ischaracterized in that the exposed parts of said segments are describedby concave shapes.
 11. A lightning diverter according to claim 10characterized by the diverter being in the shape of a strip (103).
 12. Alightning diverter according to claim 10 characterized by a number ofthe isolated segments (105) being cross-shaped.
 13. A lightning diverteraccording to claim 10 characterized by a number of the isolated segments(105) being star-shaped.
 14. A lightning diverter according to claim 10characterized by comprising a layer of material (501) increasing thestiffness of the lightning diverter in the direction along the strip(103).
 15. A lightning diverter according to claim 10 characterized bycomprising an outermost layer of double sided adhesive tape (401).
 16. Alightning diverter according to claim 10 characterized by the segments(105) being preferably made of metal.
 17. A lightning diverter accordingto claim 10 characterized by the electrically non-conductive material(201) being preferably made of an adhesive.
 18. A blade for a windturbine, the blade comprising a fiber reinforced blade shell (1001) andmeans for grounding a lightning-induced electrical current, where theblade is equipped with at least one diverter strip (103), wherein saidat least one diverter strip (103) is produced by a method comprising thesteps of: a) making of a plurality of holes (102) in a plate (101) of anelectrically conductive material, b) filling said holes (102) at leastpartly with one or more electrically non-conductive materials, c)dividing the plate (101), thereby obtaining a layer of electricallynon-conductive material (201) with a plurality of isolated segments ofelectrically conductive material (105).